Test indicator for substances in liquids

Abstract

An indicator is disclosed, which is intended for detecting at least one test substance in a test medium, comprising a carrier and a reaction system consisting of at least a first reactant and a second reactant, applied separately on the carrier, said first reactant being intended to travel by diffusion to the second reactant through a parth in the carrier, soaked by the test medium, while reacting with the test substance. The indicator is characterized in that the first reactant is applied within at least one limited locality, while the second reactant is applied within at least one locality, on a varying distance from the locality of the first reactant.

We claim: 
     
       1. A device for indicating the presence of a defined substance in a liquid test medium comprising a substantially inert permeable substrate of substantially uniform thickness, a first reagent deposited in a first area of said substrate and being capable, upon contact with said test medium, of releasing a mobile substance capable of reacting with said defined substance, and a second reagent deposited in a second area of said substrate remote from said first area, and said second reagent being capable of changing color upon contact with said mobile substance, certain portions of said second area being more remote from the nearest portion of said first area than are other portions of said second area. 
     
     
       2. The device claimed in claim 1 wherein one of said first and second areas is smaller than the other. 
     
     
       3. The device claimed in claim 1 wherein one of said areas comprises a series of concentric circular bands and the other is located at the center of said concentric bands. 
     
     
       4. The device claimed in claim 3 wherein one of said areas is located on one side of said substrate and the other area is located on an opposite side of said substrate. 
     
     
       5. The device claimed in claim 1 wherein the areas are bands on the surface of the substrate. 
     
     
       6. The device claimed in claim 5 wherein said bands diverge. 
     
     
       7. The device claimed in claim 5 wherein the bands are on opposite sides of the substrate and are perpendicularly positioned with respect to one another.